1. Field of the Invention
The present invention relates to a soft start fire pump controller for controlling the voltage of an electric fire pump during start up and shut down.
It has been found that electric motors which drive fire pumps in multi-story buildings draw large amounts of electrical power when brought on line. In addition, turning the motors on and off creates radical pressure changes in the water pipes. These radical pressure changes can result in a condition commonly referred to as water hammer. Water hammer can injure individuals who are using a standpipe hose, and damage the equipment in the buildings.
As a result, reduced voltage starting has been developed to control the start up and shut down phases of fire pump motors. Reduced voltage starting can be achieved with specially wound motors, or by adding resistors and/or transformers in series with the motor windings. Of these two methods, adding power control devices, i.e., resistors and/or transformers, in series with the motor windings is preferable because it can be used with any type of motor. These devices known as reduced voltage starters reduce normal starting power during the motor acceleration but only remove all power during the shut down phase of a fire pump motor.
The present invention relates to a soft starter which softly stops and, in addition, incorporates a pause period during the shut down phase of the fire pump motor to test for pump demand signals. Since the voltage is held at a preset intermediate level during the pause period, the soft starter can easily return the fire pump motor back to full voltage without causing radical changes in the water pressure.
2. The Prior Art
Reduced voltage devices are known to control the voltage during start up of fire pump motors, for example, by connecting resistors, reactors or autotransformers in series with the motor windings. These devices are triggered by pressure sensors which monitor the pressure in a building's water lines. If the pressure drops, for example, by the activation of a sprinkler head or standpipe hose, the pressure sensor initiates the reduced voltage starter. The reduced voltage starter would provide a less than line voltage to the motor and after a fixed time delay, bypass the reduced voltage equipment and directly connect the motor to the pump at full voltage. The reduced voltage starter would jump to 100% voltage and continue to operate the motor at 100% full voltage for a predetermined minimum period of time or until the pressure sensors indicate that pressure has been restored in the system, whichever is longer.
Once pressure is restored, the reduced voltage starter would disconnect the motor completely. Subsequently, if the pressure sensors indicate a low pressure condition, the reduced voltage starter will re-initiate the sequence to bring the motor back to full voltage and full running speed. A deficiency exists with the known systems in that starting and, particularly, stopping the motor may cause abrupt fluctuations in the water pressure possibly injuring fire fighting personnel and/or damaging fire protection equipment, water lines, pipes, valves, etc.
The applicant has previously patented fire pump control mechanisms for electric and diesel engines in U.S. Pat. Nos. 3,859,565 and 4,611,290. Other fire pump control mechanisms are disclosed in U.S. Pat. Nos. 3,974,879 and 3,544,235. Other control mechanisms are disclosed in U.S. Pat. Nos. 3,576,292, 3,591,077, 4,907,620, 3,953,152, 4,278,110, 4,344,741, and 4,124,332. However, none of these devices overcome the problems associated with prior art soft starters.